Implantable valve prosthesis for treating venous valve insufficiency

ABSTRACT

A valve prosthesis for percutaneous placement within a vein is disclosed that includes a valve scaffold and a backflow barrier. The valve scaffold is of a shape memory or resilient material and the backflow barrier is a flap of flexible material attached to the valve scaffold. The valve prosthesis is operable to alternate between open and closed configurations in response to changes in retrograde blood flow pressure. In the open configuration, the valve scaffold has a frustoconical coil shape of consecutive windings with open spaces therebetween and the backflow barrier allows antegrade blood flow through the open spaces. In the closed configuration, the consecutive windings of the valve scaffold are collapsed such that the valve scaffold has a substantially flat profile and the backflow barrier covers the opens spaces of the flattened valve scaffold to prevent retrograde blood flow from leaking there through.

FIELD OF THE INVENTION

The invention relates to valve prostheses for percutaneous placementwithin a vein.

BACKGROUND OF THE INVENTION

Venous valves are found within native venous vessels and are used toassist in returning blood back to the heart in an antegrade directionfrom all parts of the body. The venous system of the leg for exampleincludes the deep venous system and the superficial venous system, bothof which are provided with venous valves which are intended to directblood toward the heart and prevent backflow or retrograde flow which canlead to blood pooling or stasis in the leg. Incompetent valves can alsolead to reflux of blood from the deep venous system to the superficialvenous system and the formation of varicose veins. Superficial veinswhich include the greater and lesser saphenous veins have perforatingbranches in the femoral and popliteal regions of the leg that directblood flow toward the deep venous system and generally have a venousvalve located near the junction with the deep system. Deep veins of theleg include the anterior and posterior tibial veins, popliteal veins,and femoral veins. Deep veins are surrounded in part by musculaturetissues that assist in generating flow due to muscle contraction duringnormal walking or exercising. Veins in the lower leg of a healthy personmay range from 0 mm Hg to over 200 mm Hg, depending on factors such asthe activity of the body, i.e., stationary or exercising, the positionof the body, i.e., supine or standing, and the location of the vein,i.e., ankle or thigh. For example, venous pressure may be approximately80-90 mm Hg while standing and may be reduced to 60-70 mm Hg duringexercise. Despite exposure to such pressures, the valves of the leg arevery flexible and can close with a pressure drop of less than one mm Hg.

FIGS. 1A-1B are schematic representations of blood flow through ahealthy native valve 104 within a vein 100. Valves within the venoussystem are configured in a variety of shapes that depend on anatomicallocation, vessel size, and function. For example, the shape of thevenous valve may include leaflets or leaflets with sinuses. The naturalvenous valve leaflet configuration referenced herein is for clarity offunction and is not limiting in the application of the referencedembodiments. Venous valve 104 controls blood flow through lumen 102 ofvein 100 via leaflets 106, 108. More particularly, venous valve 104opens to allow antegrade flow 112 through leaflets 106, 108 as shown inFIG. 1A. Venous valve 104 closes to prevent backflow or retrograde flow114 through leaflets 106, 108 as shown in FIG. 1B.

Veins typically located in the leg can become distended from prolongedexposure to excessive pressure and due to weaknesses found in the vesselwall causing the natural venous valves to become incompetent leading toretrograde blood flow in the veins. Such veins no longer function tohelp pump or direct the blood back to the heart during normal walking oruse of the leg muscles. As a result, blood tends to pool in the lowerleg and can lead to leg swelling and the formation of deep venousthrombosis and phlebitis. The formation of thrombus in the veins canfurther impair venous valvular function by causing valvular adherence tothe venous wall with possible irreversible loss of venous function.Continued exposure of the venous system to blood pooling and swelling ofthe surrounding tissue can lead to post phlebitic syndrome with apropensity for open sores, infection, and may lead to limb amputation.

Chronic Venous Insufficiency (CVI) occurs in patients that have deep andsuperficial venous valves of their lower extremities (distal to theirpelvis) that have failed or become incompetent due to congenitalvalvular abnormalities and/or pathophysiologic disease of thevasculature. As a result, such patients suffer from varicose veins,swelling and pain of the lower extremities, edema, hyper pigmentation,lipodermatosclerosis, and deep vein thrombosis (DVT). Such patients areat increased risk for development of soft tissue necrosis, ulcerations,pulmonary embolism, stroke, heart attack, and amputations.

FIG. 2 is a schematic representation of blood flow through anincompetent venous valve. Valve leaflets 106, 108 do not completelyclose and thus allow some venous blood to flow in a retrogradedirection. The retrograde flow or backflow 114 leaks through venousvalve 104 creating blood build-up that eventually may destroy the venousvalve and cause a distended area or venous wall bulge 110. Morespecifically, the vessel wall of vein 100 expands into a pouch or bulge,such that the vessel has a knotted appearance when the pouch is filledwith blood. As the bulging progresses, vein 100 becomes further enlargedand valve leaflets 106, 108 move farther apart, allowing even more bloodto backflow. Thus, once valve 104 becomes incompetent, the venousinsufficiency/incompetency progressively worsens. The distended vesselwall area may occur on the outflow side of the valve above leaflets 106,108 as shown in FIG. 2, and/or on the inflow side of the valve belowleaflets 106, 108. After a vein segment becomes incompetent, the vesselwall dilates and fluid velocity there through decreases, which may leadto flow stasis and thrombus formation in the proximity of the venousvalve.

Repair and replacement of venous valves presents a formidable challengedue to the low blood flow rate found in native veins, the very thin wallstructure of the venous wall and the venous valve, and the ease andfrequency of which venous blood flow can be impeded or totally blockedfor a period of time. Surgical reconstruction techniques used to addressvenous valve incompetence include venous valve bypass using a segment ofvein with a competent valve, venous transposition to bypass venous bloodflow through a neighboring competent valve, and valvuloplasty to repairthe valve cusps. These surgical approaches may involve placement ofsynthetic, allograft and/or xenograft prostheses inside of or around thevein. However, such prostheses have not been devoid of problems, such asthrombus formation and valve failure due to leafletthickening/stiffening, non-physiologic flow conditions,non-biocompatible materials and/or excessive dilation of the vesselswith a subsequent decrease in blood flow rates. In addition, many venousvalve prostheses include leaflets and/or hinged flaps and are similar tovalves placed into the heart, which are complex and designed for highblood pressures associated with the heart instead of lower venous bloodpressures associated with veins in the lower extremities.

Percutaneous methods for treatment of venous insufficiency are beingstudied, some of which include placement of synthetic, allograft and/orxenograft prosthesis that suffer from similar problems as the surgicallyimplanted ones discussed above.

In light of these limitations, there is a need for an improved device torestore normal venous circulation to patients suffering from venousvalve insufficiency. The present disclosure is directed to a one-wayvalve prosthesis that may be percutaneously placed within a vein.

BRIEF SUMMARY OF THE INVENTION

Embodiments hereof are directed to an one-way venous valve prosthesisfor percutaneous placement within a vein. The prosthesis has a bodyportion including a valve scaffold and a backflow barrier. The bodyportion is operable to alternate between an open configuration whereinthe valve scaffold has a frustoconical coil shape of consecutivewindings with open spaces therebetween, and a closed configurationwherein the consecutive windings of the valve scaffold are collapsedsuch that the valve scaffold has a flat profile. The backflow barrierallows blood flow through the open spaces between consecutive windingsof the valve scaffold when the body portion is in the open configurationand the backflow barrier covers the open spaces between consecutivewindings of the valve scaffold to prevent blood flow through the valveprosthesis when the body portion is in the closed configuration.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following description of embodiments hereof asillustrated in the accompanying drawings. The accompanying drawings,which are incorporated herein and form a part of the specification,further serve to explain the principles of the invention and to enable aperson skilled in the pertinent art to make and use the invention. Thedrawings are not to scale.

FIGS. 1A-1B are schematic representations of blood flow through ahealthy valve within a vein.

FIG. 2 is a schematic representation of blood flow through anincompetent valve within a vein.

FIG. 3 is a perspective view of a valve prosthesis according to anembodiment hereof, wherein the valve prosthesis is in a preset openconfiguration.

FIG. 3A is a side perspective view of a valve scaffold of the valveprosthesis of FIG. 3 shown in the preset open configuration.

FIG. 4 is a perspective view of the valve prosthesis of FIG. 3, whereinthe valve prosthesis is in a closed configuration to prevent blood flowthere through.

FIG. 4A is a top view of the valve scaffold of the valve prosthesis ofFIG. 4.

FIG. 5 is a schematic sectional view of the valve prosthesis shown inFIG. 3 being delivered to a treatment site within a vein, wherein theprosthesis is in a delivery configuration.

FIG. 6 is a schematic sectional view of the valve prosthesis shown inFIG. 3 placed within a vein, wherein the prosthesis is in the openconfiguration.

FIG. 7 is a schematic sectional view of the valve prosthesis shown inFIG. 3 placed within a vein, wherein the prosthesis is in the closedconfiguration.

FIG. 8 is an example of a delivery system for delivering the valveprosthesis shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments of the present invention are now described withreference to the figures, wherein like reference numbers indicateidentical or functionally similar elements. The terms “distal” and“proximal” are used in the following description with respect to aposition or direction relative to the treating clinician. “Distal” or“distally” are a position distant from or in a direction away from theclinician. “Proximal” and “proximally” are a position near or in adirection toward the clinician.

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Although the description of the invention is in the contextof treatment of blood vessels such as the superficial and deep veins ofa leg, the invention may also be used in any other body passagewayswhere it is deemed useful. Furthermore, there is no intention to bebound by any expressed or implied theory presented in the precedingtechnical field, background, brief summary or the following detaileddescription.

Referring to FIGS. 3, 3A, 4 and 4A, a venous valve prosthesis 316 fortreating chronic venous insufficiency according to an embodiment hereofis shown. Valve prosthesis 316 has a body portion 318 that includes avalve scaffold 320 and a backflow barrier 322. Valve scaffold 320 ofbody portion 318 is attached to a self-expanding annular anchor or stent325 for securing valve prosthesis 316 within a vessel, as will bedescribed in more detail below with respect to FIG. 6. When implanted invivo valve prosthesis 316 opens and closes in response to changes inantegrade and retrograde blood flow to mimic venous valve operation.Body portion 318 of valve prosthesis 316 is operable to alternatebetween a preset open configuration shown in FIG. 3, in which backflowbarrier 322 allows blood flow through valve prosthesis 316, and a closedconfiguration shown in FIG. 4, in which backflow barrier 322 preventsblood flow through valve prosthesis 316.

FIG. 3A illustrates valve scaffold 320 separated from valve prosthesis316 as shown in FIG. 3. In the preset open configuration, valve scaffold320 is a wire-like or tubular structure 330 having a frustoconical coilor spring shape formed by a series of consecutive loops or windings 324with open spaces 326 therebetween. A single winding 324 of valvescaffold 320 may also be described mathematically as a helical toruswherein the generally toroidal or “doughnut” shape is formed out ofplane by one turn of a helix. The outer diameters of windings 324gradually decrease from a base winding 324′ to a nose winding 324″. Whenvalve prosthesis 316 is placed within a vein in vivo nose winding 324″of valve scaffold 320 is situated upstream of base winding 324′ of valvescaffold 320 such that antegrade blood flow is in a direction indicatedby arrow 328. Although four windings 324 are shown in the embodiment ofFIG. 3A, more or fewer windings may be used without departing from thescope of the present invention.

In various embodiments in accordance herewith, wire-like structure 330may be solid or hollow and have a circular cross-section with a diameterbetween 0.002 inches and 0.015 inches. In another embodiment, thecross-section of wire-like structure 330 may be an oval, square,rectangular, or any other suitable shape. Wire-like structure 330 ofvalve scaffold 320 is formed from a biocompatible shape memory materialor a biocompatible resilient material that permits valve scaffold 320 tobe deformed during delivery and/or during valve operation and thereafterreturns valve scaffold 320 to the preset longitudinally extended shapedepicted in FIG. 3A, which may also be referred to as a frustoconicalcoil shape. A “shape memory” material as used herein refers to amaterial that exhibits shape memory, which is the ability of thematerial to be severely deformed and then returned to its original shapesimply by a change in temperature, and/or super (or hyper)-elasticity,which is an almost rubber-like flexibility demonstrated by the materialto spring back to its original shape after loading that does not requirea change in temperature. A heat or thermal treatment may be used to setthe shape of wire-like structure 330 of a shape memory alloy, such asnitinol. For example, wire-like structure 330 of nitinol may be presetor shape-set into the frustoconical coil shape shown in FIG. 3A using anoven set to, by e.g., 525° C. In another embodiment, a shape memory toreturn to the frustoconical coil shape may be imparted to a polymer thatforms wire-like structure 330, such as any of the polymers disclosed inU.S. Pat. Appl. Pub. No. 2004/0111111 to Lin, which is incorporated byreference herein in its entirety. “Resilient” and “resilience” as usedherein to refer to a material for forming wire-like structure 330 meansthe structure formed of the material is capable of recovering anoriginal set shape or form after being elastically stretched, deformed,compressed, or the like. In an embodiment, wire-like structure 330 ofvalve scaffold 320 may be made from a metallic material having a highresilience to return to the frustoconical coil shape after bearing aload. In addition, a mechanical memory to return to its original shapeafter being loaded may be imparted to wire-like structure 330 by thermaltreatment to achieve a spring temper in stainless steel or cobaltchromium alloys, for example Conichrome®, Phynox® and Elgiloy®.

Backflow barrier 322 is a continuous flap 332 of a non-thrombogenicflexible material attached to wire-like structure 330 of valve scaffold320. Prior to attachment to wire-like structure 330, flap 332 may have arectangular shape. In another embodiment, flap 332 may have the form ofa spiral-cut circle prior to attachment to wire-like structure 330. Asused herein, a flap is a moveable piece of flexible material that has atleast a portion of an edge thereof attached to wire-like structure 330.Accordingly, a first inner edge 334 of flap 332 is attached to wire-likestructure 330 while a second outer edge 336 of the flap 332 isunattached to valve scaffold 320 such that flap 332 is movable by bloodflow as discussed further below. Inner edge 334 of flap 332 may beattached to wire-like structure 330 by any suitable means known to thoseskilled in the art, for example and not by way of limitation, welding,adhesive, overmolding, suture, or mechanical coupling. In oneembodiment, wire-like structure 330 may extend within a hem or fold offlap 332 extending along inner edge 334. Backflow barrier 322 extendsfrom nose winding 324″ to base winding 324′ of wire-like structure 330to be attached by first inner edge 334 for the entire coiled length ofvalve scaffold 320. In an alternate embodiment, the backflow barrier maycover less than the entire coiled length of the valve scaffold. Flap 332has a thickness between 0.0005 inches and 0.0050 inches. Flap 332 may beformed from a biocompatible, non-thrombogenic material such as but notlimited to expanded polytetrafluoroethylene (ePTFE),polytetrafluoroethylene (PTFE), Dacron, silicone, and polyesters. Suchthin and lightweight materials minimize the amount of pressure or bloodflow required to open and close the valve prosthesis, thus more closelymimicking native valve operation and avoiding stasis or blood pooling atthe deployment site of the valve prosthesis, which may lead to theformation of thrombosis thereon.

As illustrated in FIG. 3, when body portion 318 of valve prosthesis 316is in the preset open configuration, antegrade blood flow represented byarrow A_(F) pushes outer edge 336 of backflow barrier 322 away fromvalve scaffold 320 so that backflow barrier 322 does not cover openspaces 326 of valve scaffold 320 and thus allows blood flow through openspaces 326 between consecutive windings 324 of valve scaffold 320. Thus,in situ, flap 332 of backflow barrier 322 is displaced in the directionof antegrade blood flow.

In FIG. 4 valve prosthesis 316 is shown in a closed configuration andFIG. 4A illustrates valve scaffold 320 separated from valve prosthesis316 as shown in FIG. 4. When body portion 318 of valve prosthesis 316 isin the closed configuration, consecutive windings 324 of valve scaffold320 are collapsed into a substantially flat or pancake-like profilehaving an approximate thickness or diameter of wire-like structure 330,and flap 332 of backflow barrier 322 covers open spaces 326 of valvescaffold 320 in order to prevent retrograde blood flow from leakingthrough valve prosthesis 316. When backflow pressure closes valveprosthesis 316, as discussed in more detail below, flap 332 is preventedfrom being displaced in the direction of the retrograde blood flow dueto interference with downstream portions of valve scaffold 320 and/orwith downstream portions of itself. Once outer edge 336 of flap 332 ispushed against wire-like structure 330 of valve scaffold 320 and/oragainst downstream portions of itself, flap 332 operates as a barrier tobackflow. Outer edge 336 of flap 332 may overlap inner edge 334 of flap332 when valve prosthesis 316 is in the closed configuration to ensurethat valve prosthesis 316 does not collapse or cave-in under backflowpressure. The width of flap 332 is thus dependent upon the number ofwindings 324 and the diameter of the target body vessel. In oneembodiment, outer edge 336 of flap 332 overlaps inner edge 334 of flap332 between one and four times the thickness of wire-like structure 330.As shown in FIG. 4, center 338 of valve prosthesis 316 may have a smallopening when in the closed configuration. Such a small opening may allowsome backflow leakage through valve prosthesis 316 that will not affectthe function of the valve prosthesis in substantially reducing refluxand preventing long-term retrograde backflow. Alternatively, center 338of valve prosthesis may be covered such that there is no opening invalve prosthesis 316 when in the closed configuration. In such anembodiment, a portion of flap 332 may be sized to cover center 338, or aflared tip (not shown) may be attached to an end of nose winding 324″ ofwire-like structure 330 to essentially plug center 338 of the valveprosthesis when in the closed configuration.

The operation of valve prosthesis 316 transitioning between the presetopen configuration of FIG. 3, in which valve scaffold 320 is in itsfrustoconical coil shape, and the closed configuration of FIG. 4, inwhich valve scaffold 320 assumes a flat profile, for regulating bloodflow through the valve prosthesis is described with reference to FIGS.5-7. FIG. 5 is a schematic sectional view of valve prosthesis 316 beingtransluminally positioned or delivered to a treatment site within a vein500 having an incompetent native valve (not shown). As shown in thedelivery configuration, valve scaffold 320 and attached backflow barrier322 resemble a ribbon would around a distal end of a delivery system,such as delivery system 801 described further below. The resilient orshape memory material of wire-like structure 330 permits valve scaffold320 to be substantially stretched and therefore compressed into a lowprofile for delivery to the treatment site. The delivery configurationdepicted in FIG. 5 allows valve prosthesis 316 to be mounted onto a lowprofile delivery system that can access small vessels such assuperficial veins. Valve prosthesis 316 is delivered to and deployedwithin vein 500 in a percutaneous manner, as described in further detailbelow, and is positioned at a target location within lumen 502 of vein500 where valve prosthesis 316 is to be implanted. It should beunderstood by one of skill in the art that methods as described hereinmay be used in any vein suffering from chronic venous insufficiency,including but not limited to superficial veins and deep veins.

When valve prosthesis 316 is deployed within vein 500, wire-likestructure 330 returns to or assumes its preset frustoconical coil shapein which it coils, winds or spirals into a series of windings 324. FIG.6 is a schematic view of valve prosthesis 316 in its open configurationdeployed within vein 500 showing valve scaffold 320 returned to itsfrustoconical coil shape. As shown in FIG. 6, valve prosthesis 316 neednot be placed adjacent to the incompetent valve but rather may beimplanted at any location along vein 500 to operate effectively.However, in an embodiment, the target location may be adjacent to thevalve leaflets of the incompetent valve. If implanted adjacent to theincompetent valve, the valve prosthesis may arrest, by means of anchoror stent 325, the progressive damage to vein 500 caused by the marginalfunction of the native valve by protecting the damaged venous wall fromfurther blood pooling, thereby allowing the native valve to scar and/orheal.

As also shown in FIG. 6, valve prosthesis 316 is secured to the wall ofvein 500 by anchor or stent 325. Anchor 325 is an annular,self-expanding structure having a sinusoidal pattern that is attached tovalve scaffold 320 in order to prevent migration of the valveprosthesis. A self-expanding anchor 325 may be deployed upon releasefrom a restraining mechanism such as a retractable sheath to bias valveprosthesis 316 into conforming fixed engagement with an interior surfaceof vein 500. In an embodiment, an anchor may be constructed of a shapememory material such as nickel-titanium (nitinol) and have any suitableconfiguration known to one of skill in the art. Examples of suitableannular support members that may be used as anchor 325 are described,for example, in U.S. Pat. No. 5,713,917 to Leonhardt et al. and U.S.Pat. No. 5,824,041 to Lenker et al., which are incorporated by referenceherein in their entirety. When used with valve prosthesis 316, anchor325 has sufficient radial spring force and flexibility to conforminglyengage the prosthesis with the body lumen inner wall. In an embodiment,a series of barbs or protrusions (not shown) may be attached to protrudefrom an outer surface of anchor 325 that lodge or embed within the veinwalls to securely fix valve prosthesis 316 within vein 500. The barbsmay be pointed or spiked or have other configurations suitable forlodging within the vein walls.

Once deployed and implanted in vein 500, valve prosthesis 316 mimicsnative venous valve operation by allowing blood to flow there through inonly an antegrade direction to thereby control backflow through lumen502 of vein 500. As described above with respect to FIG. 3, when valveprosthesis 316 is in the open configuration, antegrade blood flow A_(F)displaces backflow barrier 322 so that blood may flow through valveprosthesis 316, and more particularly through open spaces 326 betweenconsecutive windings 324 of valve scaffold 320. Generally, valveprosthesis 316 in the open configuration permits a flow of blood throughvein 500 at a rate of about 0.25 L/min to about 5 L/min.

As shown in FIG. 7, valve prosthesis 316 closes in response tosufficient retrograde blood flow pressure to have a substantially flatprofile. When blood flow through the vein changes direction, i.e.,retrograde blood flow R_(F) or backflow occurs due to changing pressuredifferentials across the new valve, the retrograde blood flow pressurecauses the frustoconical coil shape of valve scaffold 320 to flatten orcollapse and transforms valve prosthesis 316 into the closedconfiguration. More particularly as retrograde blood flow R_(F) actsagainst flap 332 of valve prosthesis 316, the force is transferred tovalve scaffold 320 and the frustoconical coil shape of valve scaffold320 is flattened such that outer edge 336 of continuous flap 332 ofbackflow barrier 322 overlaps with inner edge 334 of downstream winding324 of valve scaffold 320 whereby flap 332 covers open spaces 326between the windings 324. In this manner, backflow barrier 322 preventsor substantially reduces gravitational or retrograde blood flow R_(F)from backflowing through valve prosthesis 316. Valve prosthesis 316preferably can withstand retrograde blood flow pressures greater than150 mmHg with less than 1.0 mL/min of leakage. Valve prosthesis 316 maybe designed to withstand such retrograde blood flow pressures bymanipulating several factors, including the diameter or thickness ofwire-like member 330 of valve scaffold 320, the thickness of backflowbarrier 322, and the number of consecutive windings 324 of valvescaffold 320. In general, increased values of these factors will resultin valve prosthesis 316 being able to withstand higher retrograde bloodflow pressures. Advantageously, valve prosthesis 316 in the flattenedclosed configuration does not include pockets or sinuses that are proneto pooling backflow blood that may result in clots.

More particularly, valve prosthesis 316 is designed to collapse into theclosed configuration when the retrograde blood flow R_(F) exerts a headpressure of a given load or threshold value that is sufficient to deformvalve scaffold 320 into a flattened profile. In the preset openconfiguration valve prosthesis 316 has a resistance to closing that maydepend on several factors in addition to the shape memory or resilientmaterial from which it is formed, including material stiffness of valvescaffold 320, material thickness of valve scaffold 320, and/or thegeometry of valve scaffold 320. By manipulating these factors, valveprosthesis 316 may be designed to collapse or flatten into the closedconfiguration under predetermined pressure threshold values that dependon the particular implantation site of the valve prosthesis within thevasculature. Accordingly, the design and dimensions of valve scaffold320 may be selected such that valve prosthesis 316 collapses or flattensat a certain, predetermined pressure threshold value. For example, thediameter or thickness of wire-like member 330 of valve scaffold 320 maybe chosen such that valve prosthesis 316 will close at the predeterminedpressure threshold value. In general, greater diameters or thicknessesof wire-like member 330 will result in valve prosthesis 316 having agreater resistance to closing. In addition, the pitch or spacing betweenwindings 324 will affect the valve prosthesis's resistance to closing.In general, smaller spaces between windings 324 will result in valveprosthesis 316 having a greater resistance to closing. In addition, thematerial of wire-like member 330 of valve scaffold 320 may be chosensuch that valve prosthesis 316 will close at the predetermined pressurethreshold value. The stiffness of the material of valve scaffold 320also affects the valve prosthesis's resistance to closing, with stiffermaterials having a greater resistance to closing. Stiffness refers tothe resistance of wire-like structure 330 to deflection or deformationby an applied force. Further, the transition temperature of the materialof valve scaffold 320 will affect the valve prosthesis's resistance toclosing. For example, when valve scaffold is formed from nitinol, thetransition temperature may be set at body temperature such that valveprosthesis 316 has a higher stiffness and therefore a greater resistanceto closing upon implantation. Alternatively, the transition temperaturemay be set higher than body temperature such that valve prosthesis 316has a lower stiffness and therefore less resistance to closing whenimplanted. In one embodiment, the predetermined pressure threshold valueat which valve prosthesis will begin to close is approximately 50 mmHg.As such, valve prosthesis 316 is normally open to blood flow and willclose only when retrograde blood flow pressure exceeds the predeterminedpressure threshold value, such as when the patient stands up. When thereis insufficient retrograde blood flow pressure to maintain valvescaffold 320 in its flattened profile, the shape memory or resiliency ofthe material that forms wire-like structure 330 causes valve prosthesis316 to recover or be restored to the preset open configuration.

Embodiments of the valve prostheses described herein are preferablydelivered in a percutaneous, minimally invasive manner and may bedelivered by any suitable delivery system. In contrast to surgicallyplaced valves that require incisions and suturing at the sight of thenative valve, percutaneous delivery of a replacement valve can mitigatethromboses formed from an injury response. In general, a venous valveprosthesis in accordance with embodiments hereof having at least oneself-expanding anchor is loaded into a sheathed delivery system,compressing the self-expanding anchor(s). As previously described, theself-expanding anchors may have a sinusoidal patterned configuration ormay have an annular band configuration. Initially luminal access to adesired peripheral vein, such as the greater or lesser saphenous,femoral, or popliteal veins, is obtained using standard percutaneoustechniques such as the Seldinger technique as would be understood by oneof ordinary skill in the art. Access to the venous vasculature may beachieved through a branch of the femoral vein, or alternatively, may beachieved through a branch of the subclavian vein. A guidewire ismaneuvered to a treatment site within the vein where the valveprosthesis is to be implanted. The treatment site may be locatedupstream or downstream of leaflets of an insufficient native valve. Thedelivery system is then threaded or tracked through the vascular systemof the patient over the guidewire until the valve prosthesis is locatedwithin a predetermined target site. Once properly positioned, the sheathof the delivery system is removed to allow the anchors to self-expand,appose the venous wall, and secure the valve prosthesis within the vein.Once the venous valve prosthesis is properly positioned at the targetsite, the delivery system may be retracted and removed from the patient.

For example, FIG. 8 illustrates a schematic side view of an exemplarydelivery system 801 for delivering and deploying valve prosthesis 316 asdescribed above. Delivery system 801 includes a retractable outer shaft850 having a proximal end 852 and a distal end 856, and an inner shaft858 having a proximal end 860 and a distal end 862. Outer shaft 850defines a lumen extending there through (not shown), and inner shaft 858slidably extends through the lumen of outer shaft 850 to a distal tip864 of the delivery system. Distal tip 864 is coupled to distal end 862of inner shaft 858, and may be tapered and flexible to providetrackability in tight and tortuous vessels. In an embodiment, innershaft 858 may define a guidewire lumen (not shown) for receiving aguidewire there through or may instead be a solid rod without a lumenextending there through.

Valve prosthesis 316 is mounted on distal end 862 of inner shaft 858 asshown in FIG. 5. Valve prosthesis 316 has a compressed diameter and anincreased length when mounted on the distal end of the delivery system,and valve scaffold 320 and attached backflow barrier 322 resemble aribbon wound around inner shaft 858. Valve prosthesis 316 may be mountedon distal end 862 of inner shaft 858 by any suitable manner known in theart, such as self-expanding attachment bands, a cap coupled to thedistal end of inner shaft 858 to retain the valve prosthesis in aradially compressed configuration, and/or the inclusion of slots,ridges, pockets, or other prosthesis retaining features (not shown)formed into the exterior surface of inner shaft 858 to secure the valveprosthesis in frictional engagement with delivery system 801. Outershaft 850 covers and constrains valve prosthesis 316 while deliverysystem 801 is tracked through a body lumen to the deployment site. Outershaft 850 is movable in an axial direction along and relative to innershaft 858 and extends to a proximal portion of delivery system 801 whereit may be controlled via an actuator, such as a handle 854, toselectively release valve prosthesis 316. When the actuator is operated,outer shaft 850 is retracted over inner shaft 858 in a proximaldirection as indicated by directional arrow 866 such that valveprosthesis 316 is released and allowed to assume its preset openconfiguration. An exemplary suitable delivery system is described inU.S. Pat. No. 7,264,632 to Wright et al., which is hereby incorporatedby reference in its entirety.

Although the valve prosthesis is described herein as self-expanding forpercutaneous placement, it should be understood that the valveprosthesis may alternatively be surgically implanted within a vein in anon-percutaneous manner and may be anchored to the vein in any suitablemanner, such as via sutures, clips, or other attachment mechanisms. Forexample, in such a surgical embodiment, the valve scaffold may include aseries of drilled holes through which sutures can be passed.

In another embodiment hereof, a valve prosthesis may be designed for usein the heart such as in the aorta location as well as otherextravascular applications. In contrast to venous valve prosthesis 316,the heart valve prosthesis may be preset or heat-set in the closedconfiguration and be designed to open or expand to the openconfiguration in response to antegrade flow after it exceeds a bloodflow pressure of a threshold value.

Embodiments of the valve prostheses described herein may include ananti-coagulant coating on one or more blood-contacting surfaces of thevalve scaffold and/or the backflow barrier in order to mitigatehypercoagulability, which can be associated with foreign materials inthe bloodstream. In one embodiment, an anti-coagulant material may beembedded in the material of the valve scaffold and/or the backflowbarrier. The anti-coagulant material may be heparin, coumadin, aspirin,ticlopidine, clopidogrel, prasugrel or other suitable anti-coagulantpharmaceuticals. One suitable commercially available product by Carmedaof Sweden offers a clinically proven hemocompatible surface coatingdesigned to actively reduce thrombus formation or clotting onblood-contacting medical devices. Carmeda's BioActive Surface technologymimics the natural vessel wall to create a blood-compatible surface andalso allows for a robust heparin coating to ensure long-termbiocompatibility.

While various embodiments according to the present invention have beendescribed above, it should be understood that they have been presentedby way of illustration and example only, and not limitation. It will beapparent to persons skilled in the relevant art that various changes inform and detail can be made therein without departing from the spiritand scope of the invention. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the appendedclaims and their equivalents. It will also be understood that eachfeature of each embodiment discussed herein, and of each reference citedherein, can be used in combination with the features of any otherembodiment. All patents and publications discussed herein areincorporated by reference herein in their entirety.

1. A valve prosthesis comprising: a valve scaffold having a coil shapeof consecutive windings with open spaces therebetween, wherein the valvescaffold is formed from a first material selected from one of a shapememory material and a resilient material; and a backflow barrier that isa flap of a second material attached along a first edge to the valvescaffold and having an opposing second edge free of the valve scaffold,the second material being different from the first material, wherein thevalve prosthesis is operable to alternate between an open configurationwherein the consecutive windings of the valve scaffold form afrustoconical coil shape and the backflow barrier allows blood flowthrough the open spaces between consecutive windings of the valvescaffold, and a closed configuration wherein the consecutive windings ofthe valve scaffold are collapsed such that the valve prosthesis has asubstantially flat profile and the backflow barrier covers the openspaces of the collapsed valve scaffold to prevent blood flow through thevalve prosthesis.
 2. The valve prosthesis of claim 1, wherein the valvescaffold is formed from a wire-like structure that is preset in thefrustoconical coil shape.
 3. The valve prosthesis of claim 1, wherein anupstream free second edge of the flap overlaps with a downstreamattached first edge of the flap when the valve prosthesis is in theclosed configuration.
 4. The valve prosthesis of claim 1, wherein thevalve prosthesis collapses to the closed configuration in response toretrograde blood flow pressure of a predetermined pressure thresholdvalue that is sufficient to compress the valve scaffold into thesubstantially flat profile and the valve prosthesis returns to the openconfiguration when the retrograde blood flow pressure is insufficient tomaintain the valve scaffold in the substantially flat profile such thatthe valve scaffold returns to the frustoconical coil shape.
 5. The valveprosthesis of claim 4, wherein the predetermined pressure thresholdvalue is approximately 50 mmHg.
 6. The valve prosthesis of claim 1,further comprising: an annular self-expanding anchor attached to thevalve scaffold, wherein the anchor is operable to expand in radialapposition to a wall of a vessel.
 7. The valve prosthesis of claim 6,further comprising: barbs attached to an outer surface of the anchor,wherein the barbs are operable to lodge within the vessel wall of thevein.
 8. The valve prosthesis of claim 1, wherein the backflow barrieris a continuous flap and the second material is selected from the groupconsisting of expanded polytetrafluoroethylene (ePTFE),polytetrafluoroethylene (PTFE), Dacron, silicone, and polyester, andwherein the backflow barrier has a thickness sufficient to allow theflap to be moveable by blood flow.
 9. The valve prosthesis of claim 1,wherein the valve scaffold has a thickness between 0.002 inches and0.015 inches.
 10. The valve prosthesis of claim 1, wherein the valveprosthesis in the closed configuration is operable to remain closed inresponse to retrograde blood flow pressures of at least 150 mmHg. 11.The valve prosthesis of claim 1, wherein the valve scaffold extendswithin a hem of the backflow barrier.
 12. The valve prosthesis of claim1, wherein the valve prosthesis includes a series of consecutivewindings that extend from a nose winding to a base winding and thebackflow barrier extends from the nose winding to the base winding forthe entire coiled length of the valve scaffold.